I. Field of the Invention
This invention relates generally to the manufacture of vascular stents, and more particularly to a method of making an otherwise self-expanding stent balloon expandable.
II. Discussion of the Prior Art
Various types of stents are described in the prior art and they generally fall into one of two classes, namely, self-expanding stents and balloon expandable stents. A common type of self-expanding stent is referred to as a "Wallstent.RTM. Endoprosthesis" and is described in U.S. Pat. No. 4,655,771 to Wallsten, which is incorporated herein by reference in its entirety. It comprises a braided tubular structure of metal wires or monofilament plastic strands. The tubular structure is characterized by a longitudinal shortening upon radial expansion.
In use, such a stent may be longitudinally extended to achieve a reduced radial diameter and placed within the lumen of a delivery catheter. The delivery catheter may then be advanced through the vascular system until its distal end is located proximate a stenotic lesion to be stented. The stent is then deployed out the distal end of the catheter and when unconstrained by the catheter, it self-expands into contact with the vessel with sufficient radial force so that it is maintained in the blood vessel for an extended period of time. A suitable delivery device for a Wallstent.RTM. Endoprosthesis is shown in U.S. Pat. No. 5,026,377 to Burton et al.
An example of a balloon expandable stent is the "Palmaz.TM." balloon expandable stent described in U.S. Pat. No. 4,733,665. A balloon expandable stent may comprise a fenestrated tube of material having a low modulus of elasticity and with substantially no memory property. The fenestrations through the wall of the tube are such that when the tube is placed over the deflated balloon on a balloon delivery catheter and then is routed to the location in the vascular system where it is to be used, the inflation of the balloon deforms the stent from a reduced diameter to a larger operating diameter. The balloon is then deflated and withdrawn, leaving the stent in place.
A need exists for a stent that has the self-expanding characteristics of a braided stent, but which can be delivered over a balloon for accurate positioning and deployment. The present invention fulfills that need.